Conventionally, a wellbore is drilled using a drilling fluid that is continuously circulated down a drill pipe, through a drill bit, and upwardly through the wellbore to the surface. The next operation usually involves running a pipe string, e.g., casing, into the wellbore, and then cleaning out the wellbore, after which primary cementing operations are typically performed. The pipe is cemented in the wellbore by placing a cement slurry in the annulus between the pipe and the walls of the wellbore. The cement slurry sets into a hard impermeable mass, and is intended to bond the pipe to the walls of the wellbore whereby the annulus is sealed and fluid communication between subterranean zones or to the surface by way of the annulus is prevented.
During any of the above or other operations performed in the wellbore, a number of problems can occur, some of which are caused by the increased temperature achieved by the setting of the cement slurry, particularly in applications involving a permafrost environment or in a waterwell environment. The heat of hydration of cement is the heat generated when water (or a carrier fluid) and portland cement react. Hydration of the tricalcium silicate and tricalcium aluminate components, particularly the tricalcium aluminate, of portland cements produces an exothermic reaction that generates heat. In most cement structures, the resulting temperature increase is small because the heat is dissipated rapidly from exposed surfaces. However, in permafrost applications, dissipated heat from the setting of cement can cause damage to the surrounding environment by softening or melting the permafrost. Further, in waterwell applications where PVC pipe is used for casing, the dissipated heat can damage the pipe by softening or melting the PVC.